This invention relates to a method and a system for compressing image data photographed with a camera, etc., and in particular to a method and a system for compressing image data photographed with a camera, etc., installed on a moving vehicle.
Hitherto, there are some known ways for converting image data photographed with a camera into digital data and compressing the data for the purpose of lessening the data amount as much as possible and using for image data transmission. MPEG (Motion Picture Experts Group) standardized at present is a representative example.
An art for compressing image data and decreasing the transmission information amount is disclosed in Unexamined Japanese Patent Application No. Hei 9-55937. It is an art for compressing still and moving images separately to enhance the compression efficiency of image data with still and moving images mixed; a moving image is compressed at a high compression ratio and a still image is compressed at a low compression ratio.
In recent years, a system of photographing a front landscape, etc., with a camera installed on a vehicle and recording as image data has been developed. Here, it is possible to compress image data photographed with a camera installed on a vehicle using the image data compression process described above. To compress image data by the process when a vehicle moves, image data is compressed evenly by the moving image compression process. In the moving image compression process, it is a standard practice to use a "motion prediction" process to compress image data throughout the entire image.
However, such a motion prediction generally requires a high computation capability. It is often economically difficult to use a CPU or any other hardware having a high computation capability with a vehicle, and an image compression process not requiring a high computation capability is desired.